It is firmly established that the sperm acrosome is essential for fertilization. Males whose sperm have poorly formed acrosomes or lack acrosomes altogether are infertile. The broad, long-term objective of this research proposal is to understand the process of acrosome formation by examining the targeting, segregation, and role of acrosomal proteins during acrosome biogenesis. In light of recent advances in the field of protein targeting within the cell, is it most appropriate to consider the sperm acrosome as a regulated secretory granule. Current models propose that the segregation of proteins into regulated secretory granules occurs through the selective aggregation of proteins into a particulate complex that become the dense core of these genules. The sperm acrosome includes as part of its dense core, two high molecular weight proteins comprised of the monomer ploypeptides of 50,000 Mr (AM50) and 67,000 Mr (AM67). AM50 is a novel member of the pentraxin family of proteins and AM67 is a novel member of the complement-binding protein superfamily. In light of their relative abundance, probable ligand-binding properties, and other considerations presented in this proposal, the working hypothesis is that AM50 and AM67 are essential parts of the targeting/assembly apparatus of the developing acrosome. To examine acrosome biogenesis, five specific aims are proposed. The first is to examine the localization within the developing acrosome of several major acrosomal proteins and to determine whether these proteins bind with each other to form the dense core of the acrosome called the acrosomal matrix. The second aim is to determine whether AM50 has ligand-binding properties similar to serum pentraxins. The third aims is to determine whether Am67 has properties similar to complement-binding proteins. The fourth aim is to determine whether Am67 and mouse ssp56, a closely related protein proposed to be the sperm surface binding protein for the egg's zona pellucida, are orthologous proteins. The fifth aim is to examine various regulatory molecules to determine whether they influence the synthesis and assembly of the acrosomal components. The examine these questions, the project will use a multidisciplinary approach involving morphology, cell biology, and biochemistry. These experiments will provide new information concerning the role of these novel proteins in acrosome biogenesis and reproduction. Results from these studies could find application in the diagnosis of certain cases of male infertility.